Rotary cutting tools, such as end mills, typically have a cylindrical configuration that includes a shank portion and a cutting portion. The cutting portion contains a plurality of helically disposed cutting blades that extend from a first end (i.e., the “shank end”) of the cutting portion adjacent the shank portion, toward the opposite end (i.e., the “free end”) of the cutting portion. In some embodiments, the cutting edges of the helical teeth or blades are disposed along a substantially constant radius with respect to the longitudinal axis of the tool. In other embodiments, generally referred to as “tapered” cutting tools, the cutting portion is substantially frustoconical in shape; i.e., the cutting edge of each blade has a constantly decreasing or increasing radius with respect to the longitudinal axis of the tool as the cutting edge extends from the shank end of the cutting portion to the free end. The cutting edges of the blades in a tapered rotary cutting tool are at the same radius from the longitudinal axis of the tool in any plane through the cutting portion and perpendicular to the longitudinal axis of the tool. In still other end mill embodiments, generally referred to as “straight-fluted” rotary cutting tools, the cutting edges of the blades extend parallel to the longitudinal axis of the tool.
There are known rotary cutting tools in the art that have unequal indexing. These rotary cutting tools work in any ratio of the length of cut (LOC) to cutting diameter (D) (i.e., L-D ratio) because they have the same constant helix on all flutes. There is also known rotary cutting tools in the art that have unequal indexing and alternating helix angles on every other flute. These cutting tools have an advantage over the cutting tools with only the unequal index due the alternating tangential forces caused by the alternating helix angles. In other words, the alternating helix angles, along with the unequal indexing, helps to further reduce harmonics during a cutting operation.
However, rotary cutting tools with unequal indexing and alternating helix angles are limited by the L-D ratio in which the cutting tool can be produced. More specifically, the L-D ratio is typically limited to a maximum of 2×D simply because the flutes with the alternating helix angles will become closer to each other as the L-D ratio increases. In addition, conventional rotary cutting tools tend to decrease in cutting performance as the flutes become to close to each other, causing a large increase in cutting forces on the following flute where the flutes have become much further apart.
Therefore, it is desirable to provide a rotary cutting tool that overcomes the shortcomings of the prior art.